text:
What trajectory do I fly if bearing angle is constant?
Let's suppose I am flying at constant bearing (initial and final heading are equal and constant) relative to the geographical north pole; what kind of trajectory would I be flying?

"constant bearing" - magnetic, or true? http://aviation.stackexchange.com/questions/8000/what-are-the-differences-between-bearing-vs-course-vs-direction-vs-heading-vs-tr?rq=1

I would say true aka relative to the geographical north... I will edit the question to specify.

does the answer here answer also your question? https://aviation.stackexchange.com/a/13249/1467

The term bearing is not so clear, as the link to another answer in the comment shows.
But let's say bearing means the angle between the track (over ground) of an aircraft and a fixed location. This position usually is the magnetic or (true) geographic north, but within the context of this question, it could also be any location on earth.
If the bearing is 90° or 270° (perpendicular to fixed location), the aircraft just flies circles, in case of using the geographic north, it flies along a line of constant latitude.
If the aircraft is flying at a different angle, the trajectory is a spiral, more precisely a Rhumb line, with curls around that location and the location at the opposite side of the earth:
  (Source)
BUT due to the magnetic deviation, the magnetic field doesn't point to the (magnetic) north pole everywhere on earth.
I simulated the trajectory for a quite similar question here. The red arrows indicate where the needle of a compass points to. The black line is the trajectory for an aircraft flying a 90°-track with respect to the local magnetic field. It is just a deformed circle.
The blue line is the trajectory of an aircraft flying a 93.6°-track. This is a deformed Rhumb line, and the aircraft coming from KLAX will circle around the magnetic pole at some point like a moth around a light. (at least mathematically)


text:
Where can I find/download infos about Special Use Airpsace (SUA) around the world?
I would like to know if there are any websites where I can find information (and possibly download it) about Special Use Airpsace (SUAs) around the world in terms of time validity, geographical coordinates, flight level restrictions...
If am not mistaking, aixm.areo is a website where I can find such information regarding the European region; I would like to know if there are other websites that allow to download such infos for the rest of the world (North America, South America, Africa, Asia, Oceania....)
If you know please could you also provide some links?
Note: the following quantities should be contained:

time validity
geographical coordinates (lat/lon)
flight level restrictions

Ok I will reformulate the question; thanks for the comment!!

See airspace at each AIS, e.g. for France, the lower airspace map at AIS France. (Upper space is here). Here is the RTBA map (military, low altitude)

You need to look this up in the Aeronautical Information Publication (AIP) for each individual country. Special Use Airspaces are contained in section ENR 5 of an AIP. Many AIP's are available online. You can find a comprehensive list here: https://www.eurocontrol.int/articles/ais-online
Simply select a country, open their AIP, and navigate to the ENR 5 section.
Below is an excerpt from AIP Denmark ENR 5.1 as an example.

Be aware that far from all SUA's have fixed activation times. Some SUA's do have published activation times in the AIP, but for many others you will have to check NOTAM's to determine whether or not they are active.

source: Stack Exchange

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sort: votes


text:
What is the name of centre of mass speed of an aircraft?
I have a list of positions (X [NM], Y[NM], Z[NM]) of an aircraft. Every coordinate is given every 1 second.
I calculate the speed [knots] between two consecutive coordinates in the following way:
$S_{i+1}=\frac{\sqrt{(X_{i+1}-X_{i})^2 + (Y_{i+1}-Y_{i})^2 + (Z_{i+1}-Z_{i})^2}}{1s}3600\frac{s}{h}$
It's basically space over time.
Does this 3D speed have a specific name?

That's a trippy question :)

I dunno what you are trying to solve for there.  Yeah, technically it would solve for velocity, but I don’t know where such a calculation would be used in aviation.

I don't want to try to solve anything... I just wonder if such speed has a specific name... it seems to me strange that there are definitions for ground speed, airspeed and so on but no definition for what I consider the most intuitive and basic definition an aircraft can have...

How is this not instantaneous ground speed ?

Ground speed does not have the z-axis

That's why it's called ground speed... it's the projection of the 3d speed on the ground... thus no Z axis

It describes what the velocity vector of the aircraft centre of gravity is in relation to the surface of the earth. Ground speed is the 2-D projection of your speed on the ground, climb speed is the vertical component.
Both ground speed and climb speed are very useful parameters as such: ground speed to figure out when the aircraft arrives, climb speed to adjust engine settings etc for reaching cruise altitude with a minimum amount of fuel used. The 3-D vector sum of the two has little practical use, that is probably why it has no separate name as far as I know.
The integrated signal is of more use: what is the position in 3D of the centre of gravity of the aircraft relative to earth? Pretty useful for navigation.

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text:
Is there a list of directs and preferred routes within USA airspace?
In Europe it is possible to find a list of directs which are contained in the Appendix 4 of the Route Availability Document from the Eurocontrol website.
My goal is to find the analogous information for the US airspace. I tried to look in the FAA website but without success.
Can you please tell me a way to achieve my goal?

I don't think so. In the US, if a pilot wants direct he or she simply files that routing or asks for it. I am not aware of any published list of authorized or acceptable direct routings.

The only thing in the US that sounds similar to me are TECs. But I don't know if they're really comparable because they're short, low-level routes.

High Altitude Area Navigation Routing
Special high altitude routes allow pilots routing options for flight within the initial high altitude routing (HAR) Phase I expansion airspace. Pilots are able to fly user-preferred routes, referred to as non-restrictive routing (NRR), between specific fixes described by pitch (entry into) and catch (exit out of) fixes in the HAR airspace. Pitch points indicate an end of departure procedures, preferred IFR routings, or other established routing programs where a flight can begin a segment of NRR.

@JonathanWalters  I think you're entirely correct there, and I'd upvote that as an answer.  In the middle of the night, it's common to get direct to any fix that Center can enter into their computer, which is essentially anything out there.  No limits.

@Federico So your question may serve a larger audience, consider editing the title to change the word directs something more ubiquitous, like routes.

In the US, the National Flight Data Center (NFDC) publishes a database of preferred routes.  You can query it or download the entire database.
Here is the result of entering only BWI to PHX:

A practical resource for planning a real flight is to review the routes of previous flights.  I browse the origin and destinations, or nearby airports to my flight and select a similar aircraft to which I am flying. On FlightAware, the route is shown in the lower right.  Here's an example:

Ok yes this is basically what I was looking for!!

@FedericoGentile  I'm curious, were you more interested in the database from NFDC or searching what pilots file?

NFDC data is what I am looking for yes!

@Frederico there are also routes that are defined more at the local level (within one ARTCC). I don't know if there's a public database for them; as controllers we just issue the reroute when the strip tells us to, so if you fly between two airports a few times and always get the same reroute that could be it.

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text:
Where to download NATs (North Atlantic Tracks) information?
I am reading about NATs (North Atlantic Tracks) and I found out they are created and regulated by the following entities:

westbound flow: Shanwick Oceanic Control
eastbound flow: Gander Oceanic Control Centre

Since I cannot find their information but from other sources (non official!), my questions are:

What are their websites?
Where can I download the NATs information they generate?

Note: the information should be official and possible machine-readable.

Thanks for the information but I do not find the websites (assuming they exist). I cannot also download the data but just see the page you sent. Could you be more specific please?

You can also find NAT tracks daily via https://www.public.nm.eurocontrol.int/PUBPORTAL/gateway/spec/index.html

Your question

I cannot find information from [Shanwick Oceanic Control and Gander
  Oceanic Control] What are their websites?

Direct answer
ATC centers have no public websites in general. Aeronautical information is distributed by a fixed dedicated network, the aeronautical fixed service (AFS) and its data network AFTN.
From ICAO North Atlantic Operations and Airspace Manual (NAT Doc 007):

The agreed OTS is promulgated by means of the NAT Track Message
  via the AFTN to all interested addressees. A typical time of
  publication of the day-time OTS is 2200 UTC and of the night-time OTS
  is 1400 UTC.

FAA, other agencies and aviation blogs relay the NAT-OTS notam on the web.
You can read below if you are interested in jet streams and how the track system is rebuilt twice a day to take advantage of current winds.

Polar jet stream
The jet streams are extremely strong west winds blowing at cruise (tropopause) altitude. The polar jet streams blow at about 50/60° latitude, and the northern polar jet stream is the one blowing over the North Atlantic ocean, the busy route between North America and Europe.
According to the theory, still in discussion, the prevalent wind in altitude in this area is due to the interaction between interleaved Ferrel cells (high pressure) and polar cells (low pressure):

Atmospheric circulation (source)
(Note the tropopause is lower at the pole than at the equator.)
This results in a wind blowing from a south cell to the closest north cell, speed is often between 50 and 150 kt, but 200 kt has been seen. However, for an observer on the ground, due to Earth rotation (Coriolis force) the flow is meandering eastwards from Canada to northern Europe at an altitude of about 8-10 km, as visible on this image of today's polar jet at 250 hPa isobar:

Source: NullSchool
Colored curves are isotachs, areas of equal air speed. Blue is 0 and purple is more than 200 km/h.
The thickness of the polar jet streams is usually less than 5 km and their width a few hundreds of km. To take advantage of jet streams when flying to Europe, aircraft must be packed into this area.
Daily updated organized track system
Aircraft fuel consumption and ground speed can be significantly improved by using tailwinds when flying eastwards, and minimizing headwinds when flying westwards, rather than just following the shortest path (great circle) between two locations. The North Atlantic Organized Track System (NAT-OTS) is a set of eastbound and westbound routes over North Atlantic, computed twice a day to this effect.
Tracks to North America are named starting at letter A, tracks to Europe are named starting at letter Z. Routes for Europe are in the middle of the polar jet, routes to North America are the northernmost, where the jet is the weakest.
Today's polar jet stream and corresponding NAT-OTS (look at eastwards tracks S/T/U tightly packed in the channel where the wind is most beneficial):

NAT-OTS vs. polar jet stream at 250 hPa isobar on 17 Feb 2020. On top, blue is 0 and purple is more than 200 km/h.
Sources: NullSchool (top), SkyVector (bottom)
North Atlantic track system
ICAO guidance for planning and using this airspace between FL285 and FL420, where almost all commercial traffic occurs, is described in NAT Doc 007.
Crossing the ocean is currently done without radar surveillance and coordinated by five oceanic area control centers (OAC): Gander, Shanwick, Reykjavik, Santa-Maria and New York East. The tracks use a set of fixed entry and exist points at their extremities:

Overall structure, with entry and exist points (source)
Those points change over time when the NAT airspace is reorganized, e.g. with the adoption of HLA in replacement of MNPS.
Track system construction
The process is collaborative between airlines and ATC.
From Wikipedia:

The day prior to the tracks being published, airlines that fly the
  North Atlantic regularly send a preferred route message (PRM) to
  Gander and Shanwick. This allows the ATC agency to know what the route
  preferences are of the bulk of the North Atlantic traffic

From SKYbrary:

The night-time OTS (eastbound) is produced by Gander OAC and the
  daytime OTS (westbound) by Shanwick OAC, each incorporating any
  requirement for tracks within the New York, Reykjavik, Bodø and Santa
  Maria Oceanic Control Areas (OCAs). The OTS planners co-ordinate with
  adjacent OACs and with domestic ATC agencies to ensure that the
  proposed system is viable. They also take into account the
  requirements of opposite direction traffic and ensure that sufficient
  track/flight level profiles are provided to satisfy anticipated
  traffic demand.

and:

Following the initial construction of the NAT tracks by the
  appropriate OCA, the proposed tracks are published on an NAV Canada
  operated internet site for review and discussion by interested
  parties. One hour is allocated for this process during which any
  comments will be considered by the publishing agency and any agreed
  changes are then incorporated into the final track design.

OTS Changeover Period
From SKYbrary:

To provide a smooth transition between the night-time and the daytime
  OTS, a period of several hours is allocated between the termination of
  one system and the commencement of the next. These periods are from
  0801 to 1129 UTC and from 1901 to 0059 UTC.
During the changeover periods, some restrictions to flight planned
  routes and levels are imposed and opposite direction traffic must
  remain clear of the inbound (terminating) OTS.

Suggested (good) reading

Flying the North Atlantic Tracks, from AeroSavvy.
North Atlantic MNPS Airspace, from Airline Pilots Forum and Resource

This is a very good answer! Thanks!!!!

How often are the NOTAM updated during the day? Is it randomly or do they follow a specific schedule?

I mean, the faa link you gave me updates the NOTAM every few minutes (sometimes 10 min, 15min ...) but the content is always the same... how is it possible? Is there a logic behind that?

@FedericoGentile: The track design is a collaborative process starting with airlines providing their route preferences (after studying the weather). Then the Oceanic Centers compute tracks starting and ending at fixed waypoints, and publish them on NAV Canada website for discussion. Routes are opened, and aircraft fly for several hours. The difficulty is to change the routes while aircraft are using them. This cannot be done often, and is actually done once a day (when traffic direction changes; most aircraft flying East in the morning but West in the evening, due to passenger preferences).

@FedericoGentile: In addition, you may observe the jet streams are not changing drastically over short periods. Open the NullSchool site, I've selected the proper parameters (wind, location and altitude), then open the menu by clicking "Earth" and move by +/- 3 hours using the highlighted buttons to watch the evolution which is usually slow.

Thanks for the additional comments guys :)


text:
What are these pointy things along the taxiway?
I've noticed these blue cylinder based objects in and around the vicinity of the taxiways.

I know this isn't probable but If an aircraft knocks into one of these, will it have resilience or will it shatter?

As @tedder42 pointed out in a comment, those are taxiway lighting fixtures. Ideally, if an aircraft impacts a lighting fixture it will neither have resilience nor will it shatter. Instead it should be frangible; there should be a deliberately weak section which will break away cleanly upon impact, preventing significant damage to the aircraft. This is true for all objects and structures within taxiway and runway safety areas.
The relevant faa-regulations are Advisory Circulars 150/5220-23, Frangible Connections, and 150/5345-46, Specification for Runway and Taxiway Light Fixtures. AC 150/5220-23 "does not constitute a regulation and is not legally binding in its own right." However, AC 150/5345-46 "is mandatory for lighting or projects funded under the Airport Improvement Program (AIP) with revenue from the Passenger Facility Charges (PFC) program."
AC 150/5345-46 includes the following requirement:

3.4.2.1 Yield Device
a. Each elevated light fixture must have a yield point near the point or position where it attaches to the base plate or mounting stake.

The yield point must be no more than 1.5 inches (38 mm) above the threaded interface of the elevated light cover (see AC 150/5345-42 for more information). See AC 150/5340-30 for additional information about light fixture yield point above grade location.
The yield point must give way before any other part of the fixture is damaged, and must withstand a bending moment of 150 foot-pounds (203 Newton-meters (N-m) without failure.
The yield point must cleanly separate from the mounting system before the bending moment reaches 500 foot-pounds (678 N-m).

[snip]
b. Type L-860 light fixtures may bend instead of separating. The fixture must not sway more than 1 inch from vertical under the specified wind loading.

More information and possible exceptions to the above requirements may be found in the linked documents.

Hopefully most professional pilots are competent enough to avoid hitting these things too often though?  Might not damage the aircraft, but if they keep having to shut down the taxiways in order to repair these things, that'd have a significant impact beyond the simple cost of replacement.

Hopefully pilots aren't running off the edges of runways and taxiways every day. But the standard is designed for the day when "hopefully" fails.

There are standards for everything. In this case, you're talking about the L-861T taxiway edge light.
AC 150/5345-46D "Specification for Runway and Taxiway Light Fixtures" describes how the lights should break away ("yield device"):

Each elevated light fixture must have a yield point near the point or position where the light attaches to the base plate or mounting stake.  The yield point must be no more than 1-1/2 inches (38.10 mm) above grade, must give way before any other part of the fixture is damaged, and must withstand a bending moment of 150 foot-pounds (203 Newton-meters (N-m) without failure.

There's no requirement they the lenses be anti-shatter. In fact using glass or plastic is allowed, the only discussion is about verifying the light output.
It also specifies the brightness, visibility angles, and maximum height (14 inches, except for snow banks).

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text:
What methodology did ICAO use to create the overall code nomenclature for airports?
If an airport is from North America, then it starts with K and so on.

Where did ICAO get the letters from?

Why does the Philippines region starts with A?

Why do airports in Izmir have
LTBx prefix?

Did they do some random letter ballot box?

Also why did they decide to make 27 regions?

Why does the Arctic have so many codes and why multi-letter codes?
Honoring the countries that operate the adjacent runways to the science facilities perhaps?

I wanted to ask multiple questions but how they got names questions are about the exact same stuff and probably has the same answer, and the Arctic is almost exactly about the same topic too but I don't think it really needs a separate question.

"If airport is from North America then it starts with K" or P, C, B, L, M or T.

Possible duplicate of What is the methodology for assigning airport codes?

I don't see this question as a dupe.  I think this question takes what's in the answers to the suggested dupe, and then goes on to ask, "ok, great, so now WHY did they decide to do it like THAT?"  The "what they do" is given, the "why they chose that method" is what's asked here, and not really, IMHO, answered in that question.

There is no one, easy answer for where each region (or country) got their one- or two-letter designation.  Many of them evolved over time.  When the ICAO (as an organizational body) was formed out of the international conference in Chicago in November 1944, dozens (or hundreds?) of things needed to be standardized between nations.  One of these things was a standard way to identify airports.  (Another was aircraft registrations... a minor, but related, blurb about that at the end.)
Many of these attending countries already had a "standardized letter prefix" from the 1912 convention in London regarding telecommunication call signs. For example, Canada was C (easy to understand why), and the United States was either W or K (less easy to see why, but there is history there, too -- see below). Other countries who were members to the 1912 convention had various call signs, some of which started with numbers.  These countries, obviously, did not easily convert over to a letter prefix system that ICAO was adopting.  At the end of the day, there were numerous ICAO committee meetings (and I can only imagine some heated arguments between delegates) that eventually resulted in the various regions and sub-regions we know today and that are depicted on the map below.
A small bit of history on how the USA evolved to the letter K:  In the late 1800s, when telegraph was getting under way and Morse Code was in heavy use, there were two very easy to use Morse Code letters: A (dot dash) and N (dash dot).  The US Government reserved these two letters for its military telegraph station call signs, and assigned A to the Army and N to the Navy. Makes some logical sense so far.  Of course, the civilians were wanting to get in on the revolutionary breakthrough of wired (and eventually wireless) telegraphic communications, so the US Government created a civilian set of call signs in addition to the military ones. To do this, they simply added a single dash to each Morse Code letter, and the dot-dash (A) became dot-dash-dash (W) and the dash-dot (N) became dash-dot-dash (K).
The USA now essentially had four different letter-prefix designations for its radio station call signs: A and N (military use), and W and K (civilian use). The W and K call signs were also geographically separated with K being assigned to all stations in the west, and W for all stations to the east. The "border" between K and W changed over time, eventually landing on the Mississippi river, but that's another topic.  You still see this today in your AM/FM music broadcasting and TV stations, with most stations "out west" being a Kxxx identifier.
Eventually, voice radios became very popular, and all new stations were only issued the letter K. W-stations were grandfathered in. Additionally, radio stations began to be carried onboard aircraft, and the previous military-only letter of N was eventually assigned to all airborne radios, including civilian. Aircraft began marking their exteriors with their N-xxx radio call sign.
Anyway, to make a long story short (too late?), the US was able to exert is muscle at the 1912 conference in London, and all 4 of those letter prefixes (A, N, W, and K) were retained for sole use to the US.  But 35 years later, during the formation of the ICAO and the resulting subcommittees, the US agreed to be "Letter K" for its airport designations and "Letter N" for its aircraft registrations, losing the letters W and A (at least in the ICAO books).  Also, remember that Alaska and Hawaii were not yet states, so they were both lumped into the Pacific Region [P] with sub-regional designations of PH and PA, along with all the other Pacific Region subs (PG for Guam, PM for Midway, PB for Baker, etc.).

That history is for radio callsigns, which does explain tail numbers but appear to be completely unrelated to ICAO airport codes. That CONUS got the region code K could easily be a coincidence. Do you have a specific source that says otherwise?

Unfortunately, I cannot find a source at the moment. This all comes from my memory from a semester of ICAO history back in my AvMgt college days.  However, the US had already been gravitating toward the letter K only for its broadcasting stations, and the ICAO prefixes were not only going to identify airports, but also other things like weather broadcasting stations. Since the US had many such stations already prefixed with K per previous international agreements, the US delegates easily argued to keep K as the US designation within ICAO.

Even if that is true for CONUS, it does not appear to be the case for any other region.

What does not appear to be the case?

Your proposed link between ITU radio prefixes and ICAO regions.

@StephenS, no, it only applies to some regions. Basically the various delegates asked for what sounded appropriate and ended up getting something. It's said that the OK prefix for aircraft registered in (then) Czechoslovakia came from initials of the lead delegate, because when they didn't get the prefix they originally wanted, they just said the first pair of letters that came to their mind and were not already taken…

@JanHudec That is also about radio prefixes, not airport region codes (the question here).

@StephenS, ICAO codes are about more than airports. They’re assigned to many things, including airports. But every “thing” (recognized by ICAO) in the US-CONUS region (for example) is assigned a starting letter of K. That’s because, 60 years go, the US delegates to the convention lobbied for, and were granted, the letter K. They did so because the US had already been assigned K in other intl agreements, such as the ITU. It made sense to stay with K. Some regions weren’t so lucky and have a new letter issued from scratch. Other regions kept what they had from their ITU assignments.

The bottom line is that ICAO codes for airports are VERY tightly linked to the history of radio station call sign prefixes. Many are the same, many are not, but the history of those radio codes goes a long way toward answering the question.

@Jimmy The only countries whose ITU and ICAO prefixes match are Canada (C), Ireland (EI), the former Soviet Union (U) and the United States (K). That isn't surprising since only 4 countries were large enough to get their own ICAO region code and had a one-letter ITU prefix; Ireland was obviously a coincidence. The other 200+ codes have no relation.

OK.  ?? I'm not sure that adds to nor detracts from my answer.  I don't know the history behind each and every letter.  I do know that VERY BROADLY, the convention delegates selected prefixes based on historical precedent in many cases (the radio prefixes being the most common, but not the only, precedent) and, where not feasible, many other cases had to combine some form of "close enough" and "you get something brand new altogether, sucks to be you".   It wasn't just some free-for-all "everybody pick a letter out of a hat".

I'm not aware of any published rationale for the region codes. Some have a seemingly rational basis, e.g. C for Canada, but that may be coincidence. The country code, where applicable, is obviously related to the country name in most cases.
See #1.
Izmir is in Turkey, which has region code L (Southern Europe) and country code T (Turkey).
See #1.
There are 22 regions, one for each letter except for I, J, Q and X. I'm not aware of any published rationale for this number or list. However, Q and X are often reserved for special purposes, and I is often not used because it can be confused with 1. That last isn't consistent with the use of O, which can be confused with 0, rather than J, though.
There is no region code specifically for Antarctica (I assume that's what you meant), and by treaty it cannot be part of any country, which is a case ICAO's rules don't address. Each country that builds an airport must therefore borrow a code from their home region(s).

Pardon my rather terrible sleep deprivation. I wanted to mean LT  -B-  J. I wonder why Izmir got B

You'd have to ask the DGCA that to be sure, but it appears all of Turkey's airport codes are LTAx through LTFx, so perhaps they simply assign the codes in alphabetical order?

perhaps simply dividing country through East to west and giving next letter if cities are different.

All the airports in Istanbul FIR seem to be LTBx and LTFx, while those in Ankara FIR appear to be LTAx, LTCx and LTDx. So, there may be some encoding of location there.


text:
How much does an ILS approach cost?
A statement in this question, asking how to pay fees for using the airport services, without being at the airport, inspires me to ask a question.
Quote:

(Yeah I know... you gotta pay for an ILS approach... yuk.)

How much does it cost to do an ILS Approach (for the pilot when he pays the bill)?
How much does it cost to do an ILS Approach for the airport (Electricity, Staff, Maintenance, Chart-making, ...)?
Is this listed as separate item on a bill, or is it included in the airport fee?
If it's included, how much would it be?
What percentage is to cover maintenance cost, and what is the payment for the controllers?
Are there differences between aircraft size?
Are there differences between ILS Category?

I am asking this question for any country in Europe, because, as Dan Pichelmann pointed out, in the US, ILS Approaches are still free.

Which country?  In the US, it's (still) free.

@DanPichelman Any country in Europe. Whichever country someone knows of.

Keep These Mind posted a link to the Coventry fee schedule on comments on the linked question

There is zero marginal cost to an airport for an aircraft to fly an ILS approach.  There is lots of cost to install the system, some cost to maintain it, and at least a slight cost to run it (electricity).  But none of that changes if you have airplanes flying on the loc + gs all day long, or nobody in the sky at all.  So pricing & cost aren't tightly coupled here; there would be some desire to pay off the equipment and the maintenance and such for the ILS by charging those who use it, but they'd be paying some average cost, rather than any marginal costs generated.

For New Zealand1, the Airways Pricing Framework is a document which describes how the prices are set but not the actual prices themselves (that is in a different document that it appears you have to sign up to receive). Some excerpts:

Consistent with international practice and ICAO guidelines, Airways uses aircraft weight as the basis for its charges.
En-route charges also vary with distance flown. Intrinsic to the formulae is the principle that prices should be
transparent and practicable. A simple pricing system lowers Airways’ costs and those of its customers.

For IFR approaches:

For aircraft flying IFR, the greater of the Minimum Price or:

for aircraft weights under 5 tonnes = Base Rate x MCTOW / 5
for aircraft weights 5-30 tonnes = Base Rate + Weight Rate x (MCTOW – 5)
for aircraft weights above 30 tonnes = Base Rate + Weight Rate x 5 x Square root of (MCTOW – 5)

» where the Minimum Price, Base Rate and Weight Rate are provided by the relevant price table.
Price tables provide the prices for each service and location. Price tables are provided in Airways’
standard terms and conditions
» where MCTOW is an aircraft’s maximum certified take-off weight measured in tonnes.

There are also different formulas for aerodrome services, en-route domestic, and en-route oceanic service.
More information can be found at the New Zealand Service and Pricing Framework page.
1. Yes I know that New Zealand is not a country in Europe.


text:
How to design a propeller for UAV?
I need some advice on designing a propeller for a UAV and choosing the right motor for it. I am doing a project which requires the fix-wing UAV to travel at cruise speed of 20 m/s and weighs a total of 12kg, the propeller will have to be a pusher and the aircraft has a L/D of 35 at cruise. I am told by the lecturer to ignore take off velocities as it takes off on a separate VTOL system before the propeller is activated at 300m for horizontal flight.
As a mechanical engineering student, I don't have much experience in aerodynamics. So far I've looked into blade element theory and airfoil designs, but there are many different variables to consider such as airfoil profile, pitch, angle of attack, diameter, and I'm at a bit of a loss on how to determine these values to match the UAV requirements. So I would like to ask, what is the best way I can go about doing this? The ultimate goal is to maximise flight time by designing a propeller and reducing power requirements.

Have you got to actually build this propeller? If so, what manufacturing methods do you have available?

We will not be building an actual prototype just designing as a university project.

That helps, it will give you more options. I would recommend using fixed pitch propeller as it keeps it simple (less moving parts) and it also sounds like you are mainly designing for cruise condition. When at uni I used a piece of software that did a lot of the hard work for you. I'll try and find it and let you know if I do.

I think it was this software. It has some design method info. You essentially need to work out your requirements (available diameter, required power/thrust) then adjust parameters to find an efficient prop that gives you what you need. http://www.propdesigner.co.uk/html/prop_designer.html

This is really useful, Thank you.

good to hear! How about making my answer the accepted answer?

It's been a long time since I did this but here's then general idea.

Work out your requirements.
Thrust, speed (usually cruise speed) and diameter (usually determined by the available space) being the key ones.
Use a piece of software such as this one to optimise other design parameters for your requirements.
You may also consider off-design (non-cruise) performance.

The link above also contains more details about the design process and considerations.

Try to get Xrotor to run. It has been written for designing minimum induced loss propellers, and you can input speed, power or thrust and diameter and the program will output the ideal propeller geometry, including twist over radius. Its first application were the propellers of the MLE and the Dedalus HPA.
Yes, it is written in Fortran. This makes it almost self-documenting.


text:
Can simultaneous departures be authorized from converging airports?
I am an ATC'r stationed overseas where we service two military airfields. The runways are 3 miles apart but converge. Our current regulations require aircraft from one airfield to delay in takeoff position while another aircraft is released or cleared for an approach to the other airfield, in order to protect from the missed approach point or departure route. However, our SIDS are designed to turn aircraft 45 degrees away from the other converging airport, but we are still required to wait.
We are in class G airspace with one airport 24/06 and the other, just south about 3.8 miles, on rwy 29/11. 90% of the time Rwys 24/29 are in use. The closest point of divergence, I'll have to double check for the exact distance however, the 24 departure SID is an immediate right turn off departure end, diverging at least 45 degrees from the missed approach or even departure of the southern airport in contention. Current rules require releases to be held if one or other other airports is departing aircraft however, it seems like the flight path deconflicts initially, making this unnecessary. I'll double check the distance, but our airspace isn't a factor. It's simply cutoff procedures that seem as a fail safe way of preventing an issue should the pilots heavily deviate from the SID (essentially flying rwy heading off 24) but very restrictive during departure phases.
Is there any way around this? Is it legal to clear both aircraft for departure with a SIDs that deconflict by 45 degrees from separate airfields?

What is the airport/airspace class look like? Can you maintain required separation at the closest point of divergence? Really this will boil down to local procedures, it's unlikely that even if there is a "legal" way of doing it, your airspace operations may not allow it.

Ron, thanks for responding. We are in class G airspace with one airport 24/06 and the other, just south about 3.8 miles, on rwy 29/11. 90% of the time Rwys 24/29 are in use. The closest point of divergence, I'll have to double check for the exact distance however, the 24 departure SID is an immediate right turn off departure end, diverging at least 45 degrees from the missed approach or even departure of the southern airport in contention. Current rules require releases to be held if one or other other airports is departing aircraft however, it seems like the flight path deconflicts initially,

I'm not an expert hence the comment. I'm not sure that you'll get any good answers without the SIDs on hand. ICAO specifies rules for the protected areas of instrument procedures and each type of SID has different protected area. Do the SIDs in question have overlapping protected areas? Then I guess you can't give simultaneous take offs.
Alternatively are they vertically separated eg at or below 4000 vs at or above 5000 for the closest legs? Just a couple of thoughts that might help. Interesting question by the way.

If this were in an FAA ARTCC's airspace, they'd handle them as one airport, because of their proximity.
The protected lateral airspace for an aircraft is 4 miles either side of the course to be flown. That eliminates a lot of possibilities.
In a non-radar environment, with only 3.8 miles between the airfields, you need a reduced separation rule, such as the 13/3 DME rule (7110.65 6-2-1, a3). One and two minute rules won't work, because of the convergence.
If you have a NAVAID that the departures fly over, you can use 3 miles between aircraft (faster in front), until their courses diverge.
The divergenge has to be 45 degrees or more, and the NAVAID has to be within 13 DME of both airports to  use the rule.
The 44 knot rule (7110.65 6-4-2) could possibly be used if you can maintain a minimum of five miles between the aircraft. Remember to account for any local speed restrictions (such as 250 knots below 10,000 feet) that may keep you from having 44 knots between your aircraft. Also, the 44 knot rule is based on filed true airspeed, not ground speed. But again, someone has to wait.
If this is a radar environment (I'm assuming you use 3 miles separation), you can release the second aircraft as soon as you get radar on the first (using radar contact within one mile of runway end) as long as you maintain 3 miles.
These rules are usable in either terminal or enroute environments. There may be more in 7110.65 chapter 3, but I don't go there, being a center controller.
If it's possible to post a plan view of the airspace, there's some CTO rated controllers on here that could give more definitive answers.


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What is your responsibility when a distraught pilot is on frequency?
I found the recent SeaTac incident with a suicidal pilot frightening. I myself remember being in very bad places mentally, and it got me to wonder what I should do if someone is on frequency, making dangerous maneuvers, and clearly has lost all hope and interest in life.
I looked through FAA guidelines and ICAO standards prior to posting this, and the only conclusion I could make is there is only an IMSAFE for you, and not for others.
But in the age of very realistic flight simulators, aviation can seem like a simple, beautiful, fun, and quick way to end one's life. If I am witnessing this, audibly on frequency and / or visually, what do I do? IMSAFE, but how about them?

A reference and brief summary would be helpful, perhaps https://www.seattletimes.com/seattle-news/airplane-taken-from-seattle-tacoma-international-airport-has-crashed/

Would be grateful if anyone could post a link withoud Adwall (No offense to @bitchaser, of course) :)

@Krumia Not sure if this is any better, but at least I haven't seen an adwall...

For clarification, when you say, "If I am witnessing this," from what perspective are you referring to witnessing it? As another pilot? As an air traffic controller? As NORAD? Something else?

Well, for a ground mechanic, he sure knew how to fly well :/

@reirab As a pilot, in particular.

@Cloud Not that well. He crashed. And very nearly crashed into the water earlier when he tried the roll. From the video, it looks like he came just a few feet from crashing into the water.

I'd be curious to know WHY he crashed. It did sound like he was losing fuel reallyyyyyy quickly.

This is tagged [tag:air-traffic-control], and yet in a comment you say that you want to know how you, as another pilot, should respond.  When I first saw this, I really did think you were asking as someone who works a shift in a tower.  The question should make all that clear, because there are quite a few procedures for ATC, and anyone asking that question is either not certified or should not be.

@can-ned_food I've asked about hijacking ATC procedures before... essentially what this is. They are classified.

Quite so.  That is more or less my point, @Cloud.  From what I can tell, JO 7110.65 is the most that you can get outside a clearance.  What I meant was that the question is mis-tagged, at best.

Do not respond to irrelevant chatter on aviation frequencies.
There are already way too many people who think it is ok to chit chat and joke on the radio while they are flying.
Not only does this distract the participants, but it distracts other pilots in the area and prevents other pilots from using the channel for constructive purposes.
If you are flying, focus on flying your aircraft at all times. You should not be socializing or playing amateur psychologist or doing anything else except flying.

Not disagreeing with the "too many people ... " part; but a distressed pilot who's in the air is not chit chat or a joke.

UKMonkey read my mind. Chit chat is an issue, but putting someone with dangerous intent at the yoke turns that airplane into a weapon.

Chit chat, schmit schmat, suicide, schmuicide.  All irrelevant to the task of flying my aircraft safely. This answer should be deleted.

On frequency, if control is responding to the distressed aircraft you should stay quiet and let them work the problem. This would not be a great time to ask for flight following or traffic advisories and you should expect neither. You should be listening for instructions broadcast to all aircraft in the area and possibly an announcement to change frequencies.
A controller may try and hand some aircraft off if possible to ease their load.
Depending on your situation, and if possible, it may be warranted for you to fly out of the area, or avoid it if you are inbound. In some cases ATC will work to get the aircraft to stay in an altitude block if you can hear this assignment, you should stay clear of that block.
It's not really your responsibility to play chase plane but reporting things on frequency may be warranted if the channel is free, you are not stepping on a controllers attempt to contact anyone, and the information is pertinent to the situation. Perhaps you saw the aircraft crash site from the air; if you can provide a definitive location it may warrant reporting. Saying something like, "Hey I see that guy" is not really helpful especially considering today's radar (although coverage is far from perfect) and soon to be ADS-B systems.
It is unequivocally NOT your place to attempt to contact or otherwise interact with the distressed aircraft. This will only increase confusion and create a situation where you are potentially contradicting what ATC is saying. To address your specific situation, controllers on the ground have the ability to get the required people on the line to work the problem. If someone with suicidal intentions is on the frequency controllers will respond (and in this case did respond) in a proper manner. It is not your place to attempt to talk to them as you are likely unqualified to do so and will likely worsen matters.

As a slight caveat to the above statement, there is one instance in which you as a pilot should get involved. In some areas of the country (or the world for that matter) where facilities are far apart and radio coverage at low altitudes is limited you may be in a situation where you can relay important information to a station that is with in your range but out of range of the aircraft in distress. In this case it is important to know this is the case and that you are not simply in range of an aircraft but out of range of the facility they are communicating with. If the distressed aircraft is making repeated, uniform calls with no clear response you may consider contacting approach and asking if they are aware of the situation. This is a very specific case and should be handled as a one-off on a case-by-case basis.

Is the ATC transcript available to read from this incident anywhere?

There are a bunch of YouTube videos with transcripts on them. Im not sure the NTSB has released anything yet.

I have to disagree with this. Without question your first priority is the safe conduct of your own flight, and you should never act so as to interfere with other operations. But if you're in a position to help safely, you should absolutely offer to do so in my book. If ATC is involved as in this case, respect their management of the situation (don't try to run the show). Maybe you have some educational background on suicide intervention. Or maybe you feel you can assist in some other situation. If you're willing, my vote is to offer, so long as it does not compromise safety.

@TypeIA I agree and I do mention a few cases where you should get involved but ATC has a lot of resources on had, and the chances that your suicide prevention training exceeds what ATC can get on the line is for sure an edge case and I agree it may be appropriate to speak up if that were the very specific scenario.

It can take ATC a long time to get appropriate experts involved. They don't exactly have teams of psychiatrists and pilots, qualified on all aircraft types ATC might encounter, on speed dial. If you feel qualified to help, offer; don't wait for ATC to find someone more qualified. They might not in time. Other than that I think fundamentally we're on the same page.

@TypeIA well, It actually depends on what it means "if you feel qualify to help"; many people may think that can help in one way or another. But in doing so they might doing the opposite. Plus the ATC is taking care of not that particular person alone but the safety of others on the ground and other pilots in the vicinity as well; if you congest the comm trying to change his mind you may endanger the life of others. I will stick with the procedure in that scenario. Follow ATC.

@AndreaGhilardi I agree, and said in my comment to work within ATC's guidance and let them run the show. They can provide a discreet frequency, or they can tell you to buzz off. No blanket "policy" can possibly cover every exceptional scenario and every diverse set of participants. Good judgment, ethics and professionalism are required on everyone's part for the most successful outcome. This is already expected of all pilots and controllers.

One thing I would note is that if you are in an aircraft, you are likely to be out of range of the person at some point. If you've made a connection with the suicidal pilot, it would probably not be so great if you disappeared. And if you decide to loiter in the area to continue to help, you have now kept your aircraft in danger and added one more aircraft for ATC to keep tabs of when you probably should have vacated the area.

ATC has no problem asking for help when they need it; I've been asked if I was willing to chase and identify (but not intercept, of course) other planes that busted airspace, and I've heard on LiveATC them asking folks to help locate the site of a forced landing and report condition.  I'm sure most folks would help--and ATC knows it. So, if they don't ask, it's safest to assume they don't need your help (i.e. interference).
In the particular case of a suicidal pilot, also consider that trying to play shrink while behind the stick could easily distract you enough that you are the one to crash and kill people. Leave that to the folks sitting in comfy chairs on the ground and focus on flying your own plane--preferably away from the immediate area so they can focus on the nutjob instead of you.


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Why doesn't this 767 nose paint line up with the rest of the paint?
Looking at this Boeing 767 you'll notice that the nose paint is not lined up with the rest of the paint. But the same model with the same paint scheme on the second image is fine. What is the reason for this?

It seems to match the paint from an alternative paint scheme which had a straight line between the blue and white sections lining up with the wing.

This is one of the types of questions that on the surface looks uninteresting but then you realize that you are equally intrigued yourself. There's definitely more than meets the eye here.

@user985466 -- Since we don't know that the photos were taken around the same time, we don't know whether it is the same plane or not.  Generally speaking,  your edit may sense, but not for the specific reason you gave when you made the edit (you said they weren't the same plane because the radome paint was different.)  "Just saying..."  But more to the point, the OP may actually know for a fact that these are the same plane.  If so, he/she should roll back the edit -- (and possibly add content to explain how these are known to be the same plane.)

It has a nose radome from another aircraft installed. The aircraft that donated the radome was painted with older TUI livery, where the blue/white border is straight, and in a slightly different place. The joggle in the paint scheme is the edge of the radome. If you put that radome back on the aircraft it came from, the paint lines will match up.
The original radome for that airplane was probably damaged by a bird strike or something on the ground, and they robbed one from another airplane (probably one that was down for maintenance) to dispatch it.

Here's an image of the livery with the straight line - https://www.planespotters.net/photo/1384414/ph-oyj-arke-boeing-767-304erwl

Lol, nice. I would have guessed it was a photo stitching error!

@PhilMiller it can happen with any aircraft almost. A KLM 737 flew around for months once with a Transavia nose for example.

Any nose cone is better than no nose cone :)

@EricNolan seems like you've accidentally posted the same image twice

As you look closer at the two planes there are windows closer to the nose of the planes . Also the red letters are over the windows in one pictures but not the other . And there are other things on the planes that are different .. So I think that if you looked at other pictures you would find the nose paint is the same .. Some lined up , some not lined up .. As long as it flies who cares ?.

@somebody thanks for pointing that out.  Here's the correct url for the alternate image of the plane in question - https://www.planespotters.net/photo/1380959/g-obyk-tui-airways-boeing-767-38aerwl


text:
Has any accident been prevented by bending or breaking the rules?
I wonder if there is an incident that pilots saved the plane or minimized the damage by bending or breaking the rules like Sully? (As it's known Sullenberger started the APU at first which was the 15th thing in QRH.)
Thanks in advance.

Pilots are, in fact allowed by law in 91.3(b) to deviate from any "rule" in an emergency to do whatever they see is the best course of action. It must happen often enough that the law specifically allows it...

Extracted from Ryanair's Operations Manual: "A significant number of operating practices allow the discretion to the Commander to decide how the flight should be flown. These are characterized with the need to exercise sound judgement and prudent assessment and may be referred to as sound operating practises (included under the more general heading of airmanship)"

I wouldn’t call what Sully did bending or breaking any rules per se.  Capt Sullenberger just had a very good understanding of the aircraft and it’s systems and what he was going to be needing in an emergency.

What Sully did was not exactly breaking a rule per se.

I heard somewhere that southwest 1380 did land with less flaps and faster than recommended by the procedure (and it seems to have been a good choice)

There is very, very little reporting on "prevented accidents," simply because nothing interesting happened on that flight. If the application of common sense to some unusual situation averted some bad outcome, you often don't have clear proof that "if we hadn't done ___ we could have crashed". You just know that things turned out okay. How bad they might have been is speculation.

@Ralph J: Even if you, the pilot or observer, can say "Wow, breaking that rule sure saved our butts!", there's almost certainly no official investigation of the non-crash, and no searchable database of nonexistent reports.

My soaring club requires you to make radio calls, but I once skipped those radio calls because I had one hand on the airbrakes and the other hand on the stick. If I'd attempted to make a radio call, that could have caused an accident. But something tells me that's not exactly what you were asking for. :D

One question is just what counts as a "rule". A law? "Best practices"? Industry standards?

@TerranSwett And that's exactly why most aircraft (that I've flown, at least) have the mic button mounted on the yoke/stick. No need to remove your hand from the yoke or limit what the other hand can be doing in order to make radio calls that way.

First I have to admit that I have no idea what FAA regulations said about passengers taking part in controlling an airplane in 1989, but I guess it was at least frowned upon, even if the passenger happened to be a pilot.
The United Airlines flight 232 made a stunningly successful "landing" at Sioux City airport, much due to the fact that they took an extra crew member from the cabin to control the throttles of their severely disabled aircraft.
Unfortunately 112 people lost their lives as the plane cartwheeled after a very rough touchdown, and one might ask what is so successful about that... well: 184 people survived a situation that was in subsequent simulations deemed to be impossible to manage.
The throttle operator was a UA training check airman Dennis Edward Fitch, riding as a passenger on this ill-fated flight. It has been stated in many sources again and again, that without his presence in the cockpit, the outcome would have been much worse, even the worst possible.
It just so happened, that Fitch had been practicing a similar scenario in a simulator after a fatal crash of Japan Airlines flight 123 in 1985. The reason of that crash was total loss of hydraulics, Fitch wanted to find out if an airliner could be controlled with throttles only. Luckily, it was somewhat possible.

“but I guess it was at least frowned upon”—no, it was lauded as a great and proper application of cockpit resource management!

Yes, after the accident, of course. This case has been displayed as a fine example of CRM, which not not a standard thing in the days. What I meant was before UA 232 took place.

@Jpe61 CRM was formally used by the FAA in 1979, and UA started training all crews by 1981. CRM was in full-effect for a good 8 years before UA232 happened (1989). It certainly was a "standard thing" in those days.

CRM was introduced as a concept in -79,  yet as late as in -92 FAA published a handbook where it describe "recent studies" finding CRM to be very beneficial for flight safety. In late eighties it was used for sure, but it was still developing. It still is, but now it's an "industty standard". Despite that, we still see accidents where sub par CRM plays a fatal role.

The passengers on flight 93 did not prevent a crash and loss of all on board, but they may have prevented an even worse outcome.  Passengers who were using their cell phones were breaking the rules.  But that is how they learned of the other hijackings.

@WalterMitty: If that’s true (were they breaking rules?), then it should be an answer in its own right, not a comment on this one.

There are two reasons I don't consider it an answer.  The passengers aren't pilots, and the question was about pilots.  And they didn't prevent an accident.  A crash in a field is better than burning down the Capitol, but no one on board was saved.

here's a nice talk about this flight and crew resource management

@WalterMitty also, a deliberate act of terrorism doesn't really fit the requirement of "accident".

The rules say to do whatever necessary to ensure safety of flight.

91.3 Responsibility and authority of the pilot in command.
  (a) The pilot in command of an aircraft is directly responsible for, and is the final authority as to, the operation of that aircraft.
  (b) In an in-flight emergency requiring immediate action, the pilot in command may deviate from any rule of this part to the extent required to meet that emergency.
  (c) Each pilot in command who deviates from a rule under paragraph (b) of this section shall, upon the request of the Administrator, send a written report of that deviation to the Administrator.

I think OP meant to ask about specific instances of 91.3 (b) uses where the plane was saved and wouldn't have been otherwise.

I bet a lot of pilots have anecdotal stories of violating procedures for the sake of safety. It may be harder to find a documented incident.

Doesn't 91.3(b) imply that no action that saved the plane could have violated the rules?  So the answer to the question is "No"

I think you're right @BillK . Given 91.3(b) it seems impossible to prevent an accident by bending or breaking the rules.

As pointed out above pilots may deviate from any regulation in the event of an emergency per §91.3(b).
One of the more common events is a civilian aircraft making an emergency diversion and landing at a nearby military airbase, such as this 777 flight which diverted to Erickson AB, Shemaya, AK.
The OP brings up the case of Cactus 1549.  But what Sully and Stiles did in powering up the APU first wasn’t a violation of the rules per se, though I’m sure there are plenty of odious airline sim check pilots that cut themselves on their overstarched undershirts who would disagree with this.
This even brings up an interesting discussion I once had with a flight instructor examiner I knew who had been a Air Safety adviser to Korean Airlines.  He told me he once conducted a systems discussion with a group of KAL 747 pilots in regards to understanding their systems in an emergency.  The KAL pilot corps at the time apparently handled their pilots in a very regimented and militaristic fashion.  When the chief pilot walked in, they all jumped to their feet and stood at attention, etc.
So this examiner guy walks up to the front of the group of the group and asks them: “Ok, so what is the emergency procedure for an engine fire on a 747-400?”
The entire group barks out the QRH entry for this contingency at the top of their lungs perfectly and in unison.
“Okay.......so what two things do you do in the event of an engine fire if you only have time to do two things?”
Dead silence.  The entire room stares blankly back at him like a second grader at a spelling bee asked to spell ‘photosynthesis’.
OEM approved procedures, standardized general operating practices and legal regulations for aviation are great guideline for safe and reliable operations but they can’t always cover every contingency perfectly.  A fundamental knowledge of your aircraft and it’s systems from a correlation level can come in real handy sometimes if you encounter something serious that’s not been documented.  It’s something test pilots know all too well, as it can allow them to make very judicious choices on flight test plans and handle unforeseen problems once in the air.

The company culture you described is a very effective inhibitor of proper CRM.

Yup.  And it happens out there.

This was posted as an answer, but it does not attempt to answer the question. etc etc

In 2017 an MD-83 aborted takeoff above V1.  The pilot was widely criticized for that, which was against a lot of rules and conventional wisdom.  The NTSB report determined that aborting above V1 was the most correct thing to do in this case.
https://www.planeandpilotmag.com/article/ntsb-report-how-this-pilot-saved-116-lives/#.XkzGlopOmhA

This is probably the best ever example of how braking the rules may sometimes save lives! I'm embarrased for not remembering this one...

There have been cases with incorrectly wired controls, with the aircraft doing the opposite action than such a wrongly wired control commands. Then the narrow rules about how to use the control to achieve intended action must be completely reversed, moving the stick in the opposite direction.
Doing so does not break the wider rules that cover such malfunctions. But I imagine how difficult is to realize them happening at the first place. This is the main reason I would never like to have just a robot in the cockpit.

Actually if programmed correctly, a robot would adjust quicker to any control anomaly. There certainly is the question about correct programming, there's a company whose robots I would not currently accept...

@Jpe61 Actually, it is very hard to program an algorithm to correctly reverse a control if needed, but only then. Not very easy to create a simple rule that says if things get worse then try doing less  of what you are supposed to do!

But it definitely is doable, IIRC even the venerable F-16 has such algorithms. Once the algorithm is set up properly, it will (with contemporary computing power) figure out very quickly how to adapt to different reactions from airframe.

With the judicious application of (shoot me for saying this) machine learning, the computer can and would fairly quickly figure out that applying left stick was causing the plane to roll right and begin compensating for it. Once in this "alternate mode", it would, most likely, fly the plane more correctly and more consistently than a human pilot who would have to fight years of training and muscle memory with every control input. Writing, testing and certifying such a system would be an absolute nightmare, but I believe it's possible.

Avionics systems are programmed very simply with old-fashioned and reliable feedback control techniques. Their behavior is specified in big documents written by aerospace engineers and handed to programmers. I don't think anything flying today uses "machine learning" or thinks about what it's doing.

Include such flying things as F-22, F-35, and think again. Neural network and adaptive control whatcummalem have been tested on F-16 for years and years. Just google and read.

@FreeMan very judicious. The current popular flavour of machine learning is running the training on huge datasets in datacenter, which creates a model, which you then run on the device. (Robot plane, in this case.) Your proposed system would have something akin to model training while in "live mode". Not impossible, but not what most people use machine learning for now.

You have to be very careful when you talk about algorithms and machine learning in the same breath.  If the machine learning generates an algorthm on the fly, such a system cannot be tested for reliability using classical testing methods.

For unforeseen cases, machine learning is as restricted as conventional programming. Neural network works well for cases it has been trained for, or similar. Nobody knows how else wrongly that 560 pin ELAC connector could be wired.

I will note that in maritime law there is the General Prudential Rule which states that avoiding a collision takes precedence over strict adherence to other rules and regulations.
I would have to believe that there are similar provisions in aviation rules.

I believe that the motor law where I learned to drive has the same clause.  At least, in my driving class many years ago, I was told that the law said that avoiding a collision trumped all other rules.


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Is this method to calculate a biplane's center of gravity using 57% of the biplane's gap and 23% of each wing's MAC correct?

Once you have the MAC for both wings and the CG balance point as a percentage of the MAC. connect the two CG positions with a line. Measure up between the wing Gap distance and place your center of lift (CL) at the 57% reference line. Project this location up and balance your biplane at this postion (see red lines). A CG forward of the CL makes the model more stable. Placing it aft of the CL makes model less stable.

 Source: Modelairplanenews.com
I'm trying to use this method for a Bucker Jungmeister model. The gap is 12.5 in. and the top wing MAC is 9.44 in. and the bottom wing MAC is 9.9 in. Is this the best method?

The graphic came from Model Airplane News.   https://www.modelairplanenews.com/balancing-biplanes/

I think that that 57% is just the average of the two MACs. If both MACs are equal (let's say 1) then the average is 0.5 i.e. 50%. If the upper MAC is bigger then the average is closer to it, otherwise the other way around. In your case it should be less than 50% since the lower MAC is bigger.

I think I found the answer. It seems a little more complicated. I'm grappling with the variables and math found in this graphic on Quora I found. It's from a gentleman by the name of Krishna Kumar Subramanian. https://www.quora.com/How-are-the-calculations-for-a-biplane-different-from-a-conventional-monoplane. The use of wing area seems similar to derive a Gap.  I'll try to add the graphic somehow. I'd like to know the combined MAC value.

I also found this simplified calculation method that comes from "Balancing Biplanes
by Dimitrios Katsoulis"  https://rckavalaacroteam.com/balancing-biplanes/ I am suspecting that both simplified methods are sourced from the more complicated formula demonstrated by Mr. Krishna Kumar Subramanian. Hopefully someone more knowledgeable will confirm this.

Well I was almost right: it's the average indeed but based on the wing areas instead of the chords

I think I found the answer to my own question.  I mentioned it in the comments above. It's found on Quora by Mr. Kishna Kumar Subramanian.

Source: https://www.quora.com/How-are-the-calculations-for-a-biplane-different-from-a-conventional-monoplane

I completed these calculations and was left with the problem of locating the MAC by distance or by the sweep at MACd. I'm looking for this small detail. In the meantime can anybody direct me to calculations for Biplane MAC distance from root and sweep from root datum line at the MAC location? Thanks Wally


text:
Why does an aircraft require less power when it is flying slower than the most efficient speed?
While I understand the derivation of Power required,
I fail to understand why minimum power required corresponds to a velocity that is lower than velocity corresponding to minimum thrust required.
My understanding is that Minimum Thrust is the most efficient speed an airplane should fly at and how can flying lower than that consume even lesser power.
Please correct my understanding if wrong.

Edit: While the given explanations make sense thinking about Piston driven engines, where thrust decreases with increase in velocity. I am still having trouble understanding the concept with JET engines where thrust is fairly consistent with speed. Would really appreciate if somebody could clarify

Do you mean by a mathematical or by a physical point of view? Or both?

There are two ways to look at efficiency of flight, and it depends on the objective of the flight which type off efficiency is applicable.
If the objective is to stay airborne as long as possible, we want to minimise the energy consumption per unit of time. In this case, the speed to fly at is the speed which has the minimum power required.
If the object is to fly as far as possible, we want to minimise the energy consumption per unit of distance traveled. Since energy consumed equals force (thrust) times distance, the minimum energy per unit of distance is found when the thrust and thus drag is lowest.
The minimum drag speed (most efficient for travel) is found at a speed that is higher that the minimum power speed (most efficient for staying airborne as long as possible) .
Flying at the minimum drag velocity requires more power than flying at the minimum power velocity.
For transport flights, cruising speeds are selected close to the minimum thrust speed, but holding speeds are selected close to minimum power speed.

Own work using Desmos graphing calculator

Re "cruising speeds are set close to the minimum thrust speed" - that's not true. Minimum thrust speed occurs at the same speed as $V_{L/D \ max}$. What is special about $V_{L/D \ max}$? - it is also the best glide speed; and the best glide speed is generally nowhere near the cruise speed.

@AdityaSharma best glide and max range speed are typically very close to each other. Differences are due to the fact that propulsive efficiency is not constant over the speed envelope. For best glide, only L/D matters, because there is no propulsive efficiency to take into account. For maximum range cruise, the variation with speed of the  efficiency of the propulsive system needs to be taken into account as well, but the offset from best-glide is typically low.  For operational reasons (time is money) a slightly higher speed is chosen, accepting extra fuel costs because it saves time.

@AdityaSharma see also https://aviation.stackexchange.com/q/81664/19

That's why airliner Vbg is close to their cruising speed (with flaps up).

But Aditya Sharna is still correct, because cruise speeds are nowhere near maximum range cruise speed.  They are much faster.  Other considerations than fuel consumption matter as well.

While the given explanations make sense thinking about Piston driven engines... I am still having trouble understanding the concept with jet engines.

The kind of propulsion is actually not part of the problem. And therefore I think that the easiest way to understand it is just using a... sailplane
A sailplane basically loses altitude in order to overcome aerodynamic drag: it continuously trades potential energy (thanks to the loss in altitude) with kinetic energy (which is being dissipated due to drag). When is this exchange  maximised? This exchange is obviously maximised when the sailplane loses as little kinetic energy as possible because of the drag i.e. when the drag is at its minimum (which happens to be also the point for best L/D). The relevant speed is termed "speed for best glide ratio".
Now, what happens when the sailplane reaches a thermal? Do we still need to minimise drag also in this case? No, the goal now is not only to gain as much altitude as possible but, since we don't know for how long the thermal is going to exist, the goal is also to do it in the quickest way as possible: now not only the travelled space (aka altitude aka potential energy) is important but the needed time as well; what has to be optimised now is therefore their ratio i.e. power by definition: the power extracted from the thermal.
So, if you want to:

fly as much space as possible, you must fly at the speed for minimum drag (best L/D).
fly as much time as possible, you must fly at the speed for minimum power required.

As said, note that this is a very general result not related to the particular propulsive system or aerodynamic characteristics of the airplane and therefore it applies equally well to an airplane with engine(s): obviously minimising the needed power minimises in this case the fuel consumption since that is the source of the power.
Due to the particular shape of the power required (as given for example in the plot in your question) the speed for minimum power is lower than the speed for minimum drag ($1/\sqrt{3}=0.76$ smaller to be precise) and the relevant drag is some 15.5% bigger.

Neat little trick that fixed pitch props have:  highest $\eta$ under partial power for V min power, then ... because forward speed and RPM are both higher ... higher $\eta$ at Vy!

Note that the general relationships described in this answer are true regardless of the shape of the thrust-required curve or drag-required curve-- the differences between the two speeds are just more pronounced with some shapes.

@quietflyer: yes correct, shall I update my answer or do you want do it?

Alas, the "power extracted from the thermal" can only be applied as gravitational force, "thrust" = mg × sin glide angle $\theta$.

@sophit -- it was just a comment of general interest.  I won't update it and you already implied it with phrase "or aerodynamic characteristics of the airplane" but I think it would make a nice addition to answer to point it out explicitly-- I'll leave it up to you.  Feel free to borrow/adapt any language you wish from the comment.  Maybe simply a final sentence pointing out that with curves other shapes, the exact difference between speeds will be different but the min-power-req speed will still always be lower....

This is because as speed decreases, it requires less power to produce a given amount of thrust. The following is a thrust-speed curve for a 1 watt engine:

The engine is operating at a constant propulsive efficiency ($η$) of 1 - this means that the shaft-power (RPM × Torque) gets converted into thrust-power (thrust × speed) with 100% efficiency¹. We can see that at 1 m/s, we obtain 1 newton of thrust from the 1 watt engine. The important thing to remember is that thrust is inversely proportional to speed.
If the aircraft slows down from the minimum thrust speed, it would certainly need a greater amount of thrust to oppose the drag. However, since the speed has reduced, the power required to produce that thrust has also reduced. As a result, the minimum power speed is slightly less than the minimum thrust speed - at this speed, the power required (thrust × speed) is minimum, even though thrust alone is not.

¹of course in practice, $η$ is not constant - it itself varies with speed, but the reasoning for why the minimum power speed is less than the minimum thrust speed remains the same.

Thanks for your reply. While it makes sense for propeller driven aircraft. How would you explain Jet aircraft where thrust is contents across range of velocities. Again assuming constant air density

all aircraft are moved with thrust

THRUST ACCELERATES AIRCRAFT UNTIL DRAG EQUALS THRUST

"Potential energy" of fuel is turned into thrust, no matter if it's a propeller, a rotor, a jet, or a rocket.

Minimum "power" is the lowest aircraft fuel consumption rate, in liters per second, the keep the aircraft in level flight.
Minimum drag is the airspeed at which the lowest amount of drag is produced.  This is expressed as best L/D ratio

Why are not minimum power and minimum drag speeds the same?

Because the efficiency, $\eta$, of propellers is affected by the freestream velocity or airspeed and the propeller angle of attack.
For a given RPM, propellers can produce more thrust at a lower airspeed because force, or thrust, is derived as air m(V2 - V1).  The slower the freestream, V1, the greater the thrust per unit of fuel burned.
Even though aerodynamic drag is a bit more at V min power, for the lowest amount of fuel burned, thrust = drag at V min power.
So, if you have to glide, do it at best L/D, because $\eta$ of gravity does not change with speed!!

Oh, won't somebody PLEASE make a graph of Drag vs Velocity.

You mean "thrust required" curve? That's in the question.

Yes, absolutely, thrust = drag.  That is why, at Vbg, the angle of glide (relative to horizon) is least.  "Thrust" = g × sin $\theta$.  What could be plotted on the Drag/Thrust graph is fuel consumption, which for props, will be < Vbg at its minimum due to $\eta$ factor.


text:
Does Flight Recorders store TAWS-Terrain Warning Alerts when its inhibited?
EGPWS(Enhanced Ground Proximity Warning Systems) or TAWS (Terrain Avoidance and Warning System) systems create terrain and obstacle alerts both visual and aural.
But in some configurations they can be manually inhibited to prevent nuisance alerts.
My question is are these alerts created by TAWS are being stored in the flight recorder even when they are manually inhibited?
Anyone got any tips about where should I ask this question other than here?

I think it really depends on the specific implementation of the aircraft/EGPWS computer.

It’s a question of timing. If the pilot inhibits a TAWS mode before an alert condition exists, the TAWS will not issue an alert. If no alert is issued, the FDR can’t record it as it was never issued. The FDR can only record events that show up on the data bus. The fact that the pilot did inhibit the alert mode is recorded by the FDR.
Despite the lack of a TAWS alert when inhibited, the specific data that is used by the TAWS to determine if an alert should be issued would still be sent from the other systems and that data would be recorded by the FDR.
If the pilot inhibits an alert after it is active, the FDR will record the alert and the subsequent inhibit/cancellation of alert.

This depends heavily on what aircraft it is and how the specific systems have been programmed. I'm not a pilot but I think that it would still be able to detect the alerts because all the other data that is being fed into the alert system is still being monitored, so it's easy to know whether the alert would have been triggered.
I've seen air crash investigations where they are able to see that a pilot had inhibited an alert and then they use the data that is collected alongside to determine whether any alert would have been there.
In most aircraft, the inhibit switch is a physical switch that is not emulated, this would mean that the power to the system would be cut. In that case, one could only predict whether the system would have been triggered.
The best document about this that I've found till now is this
https://www.bahamas.gov.bs/wps/wcm/connect/0cf4b5c7-d099-4320-b839-ef5e33c8e58a/AC+07-002+Flight+Recorders+%5BA%7D2011.pdf?MOD=AJPERES
I didn't read the entire document but I hope it's of help.

If that document answers this question, it would be great to summarize the relevant parts in the answer itself. Links can serve as complimentary info, but shouldn't be the main meat of the answer.

@Jamiec the link does not entirely answer the question. It provides a bit more insight to where I got my conclusion (above link) from.

Thats fine, quote the relevant section that gave you that conclusion


text:
DO-178 qualified source code obfuscation
I want to to perform obfuscation on the software that will be delivered the customer as a library or executable to prevent or at least make it difficult to de-compile the product. However some levels of the DO-178 standard requires object code to be traceable to source code and obfuscation can alter the object code or the source code based on the technique that is preferred.
My question is that if the product is a DO-178 qualified software (not the source code) to be delivered to customer for them to integrate to their software project as a library, is there any way or tool to perform obfuscation while still satisfying the standard's requirements?

"It is known that it's a good practice to perform obfuscation on the software that will be delivered the customer" is very debatable to begin with.

@Chris I updated the reason for needing the obfuscation as stated.

From a technical & safety point of view, I don't believe it is good practice to obfuscate the binary. Depending on the language and obfuscation technique used, the software's executable may run with different CPU instructions after obfuscation and therefore critical timing may be affected.

What is the assurance level of your software? What is the language? How is traceability ensured without the obfuscation?

The software is going to be tested/verified and each line of code which is not hit during the test is dead code which simply mustn't be there. Code obfuscation and avionics don't match...

@DeltaLima It is stated in the 178C 6.4.4.2.b that the source code to object code traceability is only required if the level is  DAL-A and assume the C language is being used. The CAST-12 Certification Authorities Software Team) suggests that the traceability can be performed on the non-traceable code by identifying the object code generated by the compiler that has nothing to do with the intended functionality (such as error checks or optimizations). It is not required to trace the whole source code but the object code with these patterns only.

@sophit As I understand, if the non-traceable object code (inserted by the compiler or an obfuscation tool) can be understood and verification is achieved then they can be justified. For dead code issue, some obfuscation methods only insert some certain instructions into the code that won't create a branch or jump. So if the source code does not have dead code to begin with the obfuscation won't add a new one.

@sophit So in order to create traceability the functionality of the inserted object code must be figured out first. However the obfuscation, by nature, inserts some abstruse code so it can't be easily understood thus You are right! Code obfuscation and avionics don't match!

So, it seems we came to a conclusion that there is no place for code obfuscation in avionics. @sophit would you be able to take the information from the various comments here (yours, mine, 653lover's) and craft it into a proper answer?

@653lover: so you want to write in your code something like?
X=X+10;
X=X-10;
X=X*10;
X=X/10;
print(X);

@sophit Technically yes. There are lots of methods for obfuscating a C code or even object code. Some of them works by inserting new lines of code or instructions and some other methods just alters the instructions with other new ones whilst keeping the functionality of the executable unchanged. I was wondering if there is a tool that does these kind of operations and also qualified wrt. DO-178 Tool Qualification Requirements. I do not want to add those lines manually into the source code.

@653lover: understand. Anyway as a big con I'd say that whoever will have to modify the code after you is going to hate you  Mmh, I don't know, if that piece of code has to be certified >level C then I'd be afraid of adding anything not directly related to what the code is supposed to do

@sophit What I actually had in mind was an automated pipeline that only runs when the code is going to be released. The tool would take the final source code and compiles it and then obfuscates it so it's ready to be delivered to the client. So engineers don't have to deal with mangled code or executable. Also the resulting obfuscated binary only needs to be manually investigated if the tool is not qualified.

This is far my knowledge, sorry. And if this far yours or your company's too, then maybe you should ask for an external advisor.

What does your customer have to say about it? If they're going to use you library to develop certified code, they need to know if you are obfuscating the code. The only way they wouldn't is if your library was qualified with the obfuscation in place. Getting tools qualified is time consuming and expensive. That's why qualified compilers are ridiculously expensive. To be honest, If you were trying to sell me a library like you describe, I'd look elsewhere. Certifying and more importantly maintaining certified code is hard work. I wouldn't want the headaches that your library would introduce.

@Gerry Of course the customer will be informed as the status of the final product will be written in the contract as obfuscated and qualified. I also agree that such a tool would be expensive, but in order to protect the intellectual property which is the library for this case it might be wise to use it. In order to get around the certification process I was in search of a certified tool that produces qualified library, just like how the compilers are priced and use in this field of work.


text:
XB-70 inlet duct working method
Jenkins and Landis write in their 2004 book about the XB-70, regarding its inlet duct:
"Three movable panels, positioned by two hydraulic actuators, opened or closed the throat area to meet engine air requirements; the maximum opening was 48 inches wide (doors set at 25.5 degrees) while the minimum was 19 inches (3.6 degrees)."
The doors here are the bypass doors just before the engines, jettisoning the excess air from the duct. (There is a drawing showing four, not three panels, but this is not important fot the question.)
So as far as I can understand this, when the panels opened fully (48 in), the doors too (25.5 deg). But this means the inlet sucking in lots of air but then the doors jettisoning the max amount they can. What is the reason behind it? Wouldn't be better a smaller duct from the beginning? Or I misunderstood the method here somehow?
Update: I tried to upload this pic before, but it was not working somehow. The bypass doors are somewhere near the right, about the "32.0" mark.

Can you include an image of the Illustration question for more clarification?

Interesting question. Possibly aerodynamicists found that it formed turbulent air in that section of the intake, duct at high speed, or some other places in the flight envelope, and therefore needed a door to spill this layer overboard..

Maybe this will help.
From SD 72-SH-0003 B-70 Aircraft Study Final Report Volume IV, available here: https://ntrs.nasa.gov/search?q=19950002361
The following is from pages IV-6 and IV-7. The image is from page IV-23.
My note: AIS = Air Induction Subsystem.
"The AIS of the B-70 was a multi-shock, variable area, convergent-divergent
inlet with essentially four regimes of operation...
...During take-off and low subsonic flight (up to local Mach
number 0.6), the bypass doors were closed and the throat panels fully retracted
to provide maximum air capture area. At high subsonic-low supersonic speeds
(up to local Mach number 1.1), the bypass doors were still closed while the
throat panels moved from the maximum width of 48 inches to approximately 46
inches. (Note: Throat width is sometimes identified as throat height.) At
the intermediate supersonic speeds (up to local Mach number 1.8), the bypass
doors were opened a fixed increment while the throat panels had scheduled to
an approximate width of 41 inches. Above local Mach number 1.8 and at high
supersonic speeds, the bypass doors were modulated for terminal shock control while the throat panels were scheduled as a function of local Mach
number to a minimum width of approximately 21 inches.
To maintain efficiency throughout the wide range of operating conditions from
take-off to Mach 3 cruise, the variable geometry features of the B-70 AIS
provided continuous match of inlet and engines for maximum inlet recovery and
engine thrust. As previously stated, for take-off, the inlet was at maximum
air capture area with the bypass doors closed to provide the volume of air
demanded by the engines."
The image might clarify the position of the bypass doors:

Old discussion, but: As the text says, they exist to fine-tune the position of the shock. Jettisoning air achieves that by reducing the pressure behind the inlet throat. The SR-71's inlet design has a similar mechanism, for similar reasons.

The doors are auxiliary bypass doors, most likely to provide extra air to the engines during the takeoff roll, or low speed flight, where ram air pressure at the inlet is insufficient to provide air for the engines to operate at high thrust settings.  This isn’t anything new to an XB-70.  Many aircraft use auxiliary bypass doors near the main intake to provide extra air in the conditions described above.

Those are not auxiliary intakes, as I mentioned (and the cited book also clear about this) the doors are for jettison (i.e. to let go out) the air, and not to let air inside.

Judging by the illustration, they sure do appear to be auxiliary air intakes.

I finally able to find a better picture, I uploaded it too. That clearly shows the doors are opening to the back, so no intakes. They are between the vertical stabilizers and the "fuselage". As the book wrote, they are jettisoning air. Anyway, thank you for thinking about it :)


text:
After declaring an emergency can a pilot legally resume normal navigation without landing?
If a pilot declares an emergency and then in the process of working with ATC is able to resolve the issue, would they then be able to resume normal navigation (as a non-emergency aircraft) and continue to their destination?
Scope:

USA(FAA) General Aviation regulations. Answers for other jusristictions should be made in a similar question specific to that area, I will not be awarding one of those as the answer.
During Flight.
I am not asking if it is advisable, only if it can legally be done.
I am not interested in a discussion on specific scenarios or of emergency procedures during the emergency state.
I have looked at CFR 49,B,7,830.5 for what conditions you are required to notify the NTSB and stipulate that NTSB notification is not required. I strongly suggest you read the full 830 section if you are unsure about its content before posting.

I am interested in the question since there seems to be a tendency in the US General Aviation community to not declare an emergency even though the situation merits such a declaration, based on the volume of ATC recordings and accident investigations where the pilot needs to be coached by ATC into realizing they are in an emergency situation, and possibly declaring it verbally.
As I understand it, when declaring an emergency you may violate 91.3; e.g. any regulations. You only need to report it to the FAA if they ask you, Part 91.3(c) and if it doesn't meet the reporting requirements covered in 830.5 you don't even need to report it to the NTSB.
On the NTSB reporting, my take is, it seems to focus on equipment failure or crew/passenger illness, either of which may not have been within the control/awareness of the PIC prior to the incident. This necessitates the need for tracking and isolating incidents of equipment failure so that manufacturers can improve their equipment or to suggest procedural changes to prevent re-occurrence.
I am wondering if there is a part of the laws that I missed on actions or reporting, or any punitive actions from the FAA for declaring a legitimate emergency condition. My impression is the FAA wants to be more like the DMV for aircraft rather than the Police for aircraft. I think it would benefit the general public to understand that distinction as well.

I know you specify USA, so I won't post as an answer - but here in the UK, when I did my radio telephony test one of the parts of the mock-flight was a MayDay and then subsequent cancellation of that MayDay, and the resumption of the flight.

@Dan Did you tell people in advance that this was a practice mayday?

@DJClayworth the UK radio telephony test is carried out with a computer program, not using the actual radio! Something like this

@Dan that is fine. I mainly wanted to keep the question and answers focused and not have some answers one way and others the other way which would lead to confusion.

You haven't missed anything. There's no regulation saying that if you declare an emergency that you must land, if a situation resolves itself or the actions taken mean that a flight is no longer in danger then a pilot can continue the flight as they see fit. One example would be depressurization; once the airplane descends to a safe altitude a pilot may determine that there's enough fuel to continue to the destination and opt for that. Another example would be a sick passenger that turns out to be fine, there's no reason to land because of that.
One of the reasons there's so little paperwork involved is to invite use of the system. If a pilots know there's a mountain of paperwork or costs involved with declaring an emergency, or that they will be put under scrutiny for their decision-making they are more likely to try and deal with a situation themselves, possibly leading to an avoidable accident. Regulators do not want to discourage pilots from asking for help.

As a side note: a passenger getting sick is usually a PAN PAN Medical -situation (urgency), either of the pilots being incapacitated is a an emergency (MAYDAY). Passenger medical situations that justify emergency status are not (IIRC) often survivable.

I agree with you @Jpe61, I've personally witnessed as a passenger a case where the crew thought that another passenger was having a heart attack (so did the passenger). Everyone was convinced this person was going to die, the airplane started an emergency descent, then the guy did a couple of enormous belches and realized it was just his digestion! Soon after we leveled out and climbed back up to cruising altitude.

@Jpe61 I have rarely ever heard PAN called on the live radio. Recordings are another thing. Its either Mayday or emergency.

I was surprised that I couldn't find any specific provisions for this either in the AIM or the 7110.65 (ATC bible). But anecdotally I believe the answer is "yes," and it has happened at least once - to me - without repercussion.
It was a classic VFR-into-IMC. The weather conditions and forecast were overcast, but above minimums, with patchy rain cells, but good visibility outside the rain. I assumed with the visibility I'd be able to spot any rain or low clouds and steer clear. I was wrong, and unexpectedly entered hard IMC shortly after takeoff from an uncontrolled field.
Luckily I was instrument rated, current and proficient, in a very well-equipped aircraft, and over familiar and benign terrain. Still, I called the approach facility that handles that airport and declared an emergency. But after they radar identified me and got me on an IFR clearance, the emergency condition no longer existed and so I canceled the emergency. I landed at my intended destination airport uneventfully, counted my blessings, filed my ASRS report, and that was that. I learned a lesson, and there was no follow-up from ATC or the FAA.

I'm pretty sure the ATC and FAA would rather it be an uneventful emergency and would have no good reason to make it more troublesome than it actually is.

Thank you for your answer, I do have two questions. 1) Yes what? I was very careful to ask in such a way that an answer should be only correct or incorrect. The problem with yes and no in this context is both apply.  2) Where is the mandate that an ASRS be filed and under what condition? as a non-aviation person this is the first I have heard of this document. I see that those reports are not passed to the FAA by looking at their website.

@RowanHawkins "Yes" is the answer to your title question, "After ..., can a pilot legally resume normal navigation ...?" // The ASRS report is never mandatory. It's a voluntary, anonymous safety program. Had the FAA decided to pursue enforcement action against me for a deviation, my act of writing an ASRS report would have worked in my favor to mitigate or avoid punishment. It also helped me organize my thoughts about the incident and learn from my actions (what I did right and what I did wrong). It's something any conscientious pilot should really do in such a case, but not a requirement.

I can speak as an Air Traffic Controller working for the Brazilian government. This answer is based on what ICAO`s documents say and their adjustments for Brazilian reality as proposed in ICAO. The short answer is yes! Now I explain why and what.
I work at an international airport (mainly cargo aircraft) and one single company uses here. We have a good volume of traffic for Brazilian standards (top 10 highest traffic airports in Brazil) and after several situations where a pilot declared "Pan Pan" or "May Day" we had all procedures done, call firefighters, runway reservation and stuff, but at the end there was no more emergency situation as the aircraft crew could solve the problem and could continue their flight, but we had to maintain emergency status because of a lack of rules about that.
After numerous situations like that our manager and flight company had several meetings with the National Civil Aviation Agency of Brazil (equivalent to the FAA in the US) to determine when an emergency can be cancelled. At the end all points were considered and a new standard defined.
The official rule is: The pilot in command of the aircraft, in the same way he declares an emergency, also he can declare an emergency ending. That is working very well here.
Just to finish, I can give an example. An ATR-72 in approach, about 50NM out entered a cumulonimbus cloud and declared "May Day" (that was serious stuff). At our airport we got that information and did all the procedures. After about 5 minutes the pilot said he left the CB and everything was fine. At that point you can clearly see both aspects of this situation. Under the old rules, he would have landed in "May Day" consuming a huge amount of resources, which were not needed. With the new procedure he cancelled that "May Day" and resumed normal operations.
I hope this foreign vision of an ATCO can illustrate some of this.

Thank you for your answer, I do have a question, yes what? I was very careful to ask in such a way that an answer should be only correct or incorrect. I couldn't tell from your answer if it was correct that there was no issue. The problem with yes and no in this context is both apply.

Sorry for that, I can be very precise about that. Since that consulting federal regulators, YES YOU CAN! There are several changes and rules that are only valid AFTER some kind of regulator say it is, you know how complex are compliance, so keep short I can say you that Yes you can cancel an emergency as pilot in command the same way you declares an emergency.